Field of the Invention
The present invention relates to a double-sided image reading device for reading images on both sides of a document while the document is being delivered, and an image forming device.
Description of the Related Art
Double-sided image reading devices for reading images on both sides of a document that is being delivered have been developed as image reading devices such as a scanner.
A double-sided image reading device generally has a first reading unit to one side and a second reading unit to the other side with a feeding path of a document therebetween so that an image on a first side (front side) of the document is read by the first reading unit when the document that is being delivered passes a first reading part of the first reading unit and an image on a second side (back side) of the document is read by the second reading unit when the document after passing the first reading part passes a second reading part of the second reading unit.
As a double-sided image reading device as described above, one in which a part between the first reading part and the second reading part of a feeding path of a document is a path with S-shape (hereinafter referred to as “S-shaped path”) when seen from side (when seen from the document width direction orthogonal to the feeding direction of a document D) has been proposed.
FIG. 9 illustrates a schematic structure of a double-sided image reading device including an S-shaped path.
As illustrated in FIG. 9, in a double-sided image reading device, a document D on a document tray 930 is supplied to a feeding path 940 by a pick-up roller 901, and the supplied document D is fed toward a first reading part 921 by a separation roller 902, a registration roller 903, and a feeding roller 904 along the feeding path 940. Then, an image on a first side of the document D is read by a first reading unit 911 when the document D that is being fed passes the first reading part 921.
The document D after passing the first reading part 921 is fed toward a second reading part 922 located above the first reading part 921 by a feeding roller 905. A part between the first reading part 921 and the second reading part 922 corresponds to an S-shaped path 950.
The S-shaped path 950 generally has a structure in which a lower end of a first curved path 951 in the document feeding direction that is curved obliquely upward toward the downstream from the upstream of the document feeding direction is connected to an upper end of a second curved path 952 in the document feeding direction that is curved toward the side opposite to the first curved path 951.
When the document D that has been delivered through the S-shaped path 950 passes the second reading part 922, an image on the second side of the document D is read by a second reading unit 912. Then, the document D that has passed the second reading part 922 is delivered by a feeding roller 906 and discharged to a discharge tray 931 by a discharge roller 907.
However, a structure including such an S-shaped path 950 has a problem that skew of the document D easily occurs while it is being delivered through the S-shaped path 950.
Specifically, although a tip of the document D in the feeding direction that is being delivered (hereinafter simply referred to as “tip”) Df reaches a guide 961 forming the first curved path 951 immediately after passing over the first reading part 921 in the substantially horizontal direction, since the guide 961 rises obliquely upward, the feeding direction is forced to be changed to obliquely upward when the document D contacts with the guide 961. A frictional force due to contact with the guide 961 is applied to the tip Df of the document D.
If the areas from the one end to the other end of the tip Df of the document D in the document width direction equally contact with the guide 961 when the tip Df of the document D is guided to the guide 961, there will be no significant difference in frictional force (feeding resistance) between the one end and the other end in the document width direction.
However, due to vibration while delivery propagating to the document D and vibration when the tip Df of the document D contacts with the guide 961, the tip Df of the document D sometimes flutters up and down and right and left.
If the document D continues to be guided along the guide 961 while such flutter is occurring, one end of the document D in the document width direction contacts with the guide 961 and the other end of the document D does not contact with the guide 961 or one end of the document D does not contact with the guide 961 and the other end of the document D contacts with the guide 961. Therefore, there will be a difference in frictional force, that is, feeding resistance, between the one and the other end in the document width direction and the document D tends to incline toward the direction where the feeding resistance is large.
If the tip Df of the document D reaches the feeding roller 905 while skew is occurring, the document D is delivered to the second reading part 922 by the feeding roller 905 with the skew kept and an image on the second side of the document D is read with the skew kept.
When an image on the second side of the document D is read with the skew kept, the entire read image inclines with the inclined angle according to the level of the skew and the quality of the read image for the second side of the document D is decreased if the read image is printed on a sheet or displayed on a display of a personal computer.
In addition, for example, if few skew occurs to the document D when an image on the first side of the document D is read and skew occurs when an image on the second side of the same document D is read, only the read image of the second side is inclined. If this happens, the read images on the first side and the second side of one document D seem to be imbalance to the user when the read image on the first side is compared with the read image on the second side, which leads to bad-looking.